It often is necessary to use torque limiting devices in association with other machinery or equipment to prohibit the transfer of torques above a certain preset value so that damage to associated machinery does not occur. Such devices are widely used in aircraft applications, such as actuators for moving the flaps of aircraft wings, for manually moving rotary launching devices and the like. For instance, in rotary launching devices, the devices normally are operated by power driven mechanisms. However, it may be desirable on the flight line to manually drive the associated mechanisms for limited purposes, i.e. by hand. It is desirable to prevent the application of excessive forces which might cause damage to the associated mechanisms. Therefore, when the driving torque applied exceeds a specific overload, it is mandatory in many instances that the drive mechanism immediately be locked out to prevent damage to the actuator or the associated mechanism itself.
Specifically, there are a variety of drive systems such as described above wherein it is desirable to brake an output shaft against rotation until power is supplied to an input shaft operatively connected to the output shaft. It is known to associate a brake with such structure which will hold the output shaft against rotation and which will automatically release upon sensing input torque. It also is known to have mechanism including a brake which will limit the amount of torque transmitted from an input shaft to an output shaft. For some time, prior mechanisms performed either the no-back brake operation or the torque limiting operation, but the prior mechanisms did not accomplish both by use of the same brake. In U.S. Pat. No. 4,176,733 to Twickler, dated Dec. 4, 1979 and assigned to the assignee of this invention, an assembly is disclosed utilizing a single brake which functions to provide no-back brake operation as well as torque limiting operation, with the brake being progressively released intermediate the aforesaid two conditions to permit non-braked rotation of the output shaft. This invention is directed to an assembly similar to that shown in the Twickler patent, but with certain improvements.
For instance, many such torque limiting devices are used in what is commonly termed a "broken back" system. In other words, continuous drive shafts normally are journalled and piloted between two bearings spaced axially of the shaft. However, in many applications where an input shaft and an output shaft meet at an actuator, the drive shaft means is not continuous and is "broken" or jointed at the actuator itself intermediate or between the two axially spaced bearing means. When torque limiting devices, particularly ramp-ball devices, are used in the actuator in a "broken back" system, piloting of the input and output is desirable but rarely accomplished except for the interengagement between the balls and the ramps, the ramps conventionally taking the form of pockets in opposing cam plates. The pockets themselves perform a piloting function, but manufacturing such ramp pockets within acceptable tolerances is quite expensive. With the present invention, radially extending ramp grooves are used in the torque limiting device, eliminating the expensive ramp pockets, and simple, novel piloting means are provided between the input and output.